1. Field of the Invention
The present invention relates to a liquid ejection head configured to eject liquid using a piezoelectric actuator, and a method of driving such a liquid ejection head.
2. Description of the Related Art
In recent years, in ink-jet recording technology, to suppress deformation of paper such as curling or cockling caused by a water content of ink, a technique has been investigated to eject high-viscosity ink with a low water content. In the ink-jet recording, an increase occurs in viscosity of ink located close to an ejection orifice of a nozzle that has not been used to eject ink for a long period. The increase in viscosity of ink can cause the ejection orifice to be clogged, which can cause a reduction in ejection performance or even an ejection failure. This phenomenon tends to occur in particular when the ink used is high in viscosity and contains a large amount of colorant or the like per unit volume.
One of methods of preventing ejection orifices from being clogged is to use a meniscus vibration. In this method, a meniscus is slightly vibrated using an actuator thereby stirring ink with an increased viscosity located close to an ejection orifice. Specific techniques based on this method are disclosed in Japanese Patent No. 3613297 and Japanese Patent Laid-Open No. 2009-148927.
In the technique disclosed in Japanese Patent No. 3613297, a meniscus exposed outside an ejection orifice is vibrated by an actuator with a small amplitude at a particular frequency. On the other hand, in the technique disclosed in Japanese Patent Laid-Open No. 2009-148927, a meniscus adjuster such as an electric syringe is used to first draw a meniscus in an ejection orifice in an inward direction by depressurizing a liquid chamber communicating with the ejection orifice and then vibrate the meniscus with a small amplitude.
In the technique disclosed in Japanese Patent No. 3613297, the meniscus is vibrated in a state in which the meniscus is exposed to the outside of the ejection orifice, and thus there is a possibility that ink is incorrectly ejected or scattered. Therefore, in this technique, the vibration of the meniscus is limited to that with a small amplitude. The high-viscosity ink tends to easily increase in viscosity, and thus the small amplitude of vibration of the meniscus may not surely prevent the ejection orifice from being clogged. In the technique disclosed in Japanese Patent Laid-Open No. 2009-148927, the meniscus is vibrated such that the meniscus is first drawn to an inwardly displaced position and the vibration is performed at the displaced position, and thus it is possible to vibrate the meniscus with a large amplitude. Therefore, the technique disclosed in Japanese Patent Laid-Open No. 2009-148927 is capable of preventing the ejection orifice from being clogged with high-viscosity ink more effectively than can be by the technique disclosed in Japanese Patent No. 3613297. However, in the technique disclosed Japanese Patent Laid-Open No. 2009-148927, in addition to the piezoelectric element for ejecting ink, the meniscus adjuster is disposed in a flow path between the ink tank and the recording head. The necessity of the additional provision of the meniscus adjuster results in an increase in complexity and size of the apparatus.